Vitamin C, also known as ascorbic acid, is a crucial nutrient. It plays a significant role in maintaining overall health, acting as a powerful antioxidant protecting cells from damage. Vitamin C is also essential for collagen synthesis, a protein providing structure to skin, bones, blood vessels, and connective tissues.
The Genetic Glitch
Humans, unlike most other mammals, are unable to produce their own vitamin C due to a genetic alteration. This inability stems from a non-functional version of the L-gulonolactone oxidase (GULO) gene. The GULO gene is responsible for producing the GULO enzyme, necessary for the final step in the biochemical pathway synthesizing vitamin C from glucose.
Over time, mutations within the GULO gene in the human lineage rendered it inactive, effectively turning it into a pseudogene. While the genetic remnants of the gene are still present, they no longer produce a functional enzyme. Consequently, humans must obtain their required vitamin C from external sources.
An Evolutionary Tale
The loss of the ability to synthesize vitamin C occurred in the ancestors of humans and other primates approximately 40 to 63 million years ago. This evolutionary change persisted because early primates consumed diets consistently rich in vitamin C from fruits and vegetables. With abundant external sources, internal production of vitamin C became less critical for survival.
The absence of selective pressure against the GULO gene mutation allowed it to become fixed within the primate lineage. It is also hypothesized that losing vitamin C synthesis capacity offered an energetic advantage, as the body no longer expended energy on a process sufficiently covered by diet. This highlights how evolutionary adaptations can be shaped by environmental conditions and dietary availability.
The Impact of Deficiency
The human body’s inability to produce vitamin C means that a consistent dietary intake is essential to prevent deficiency. When intake is inadequate, the most well-known consequence is scurvy, a severe condition from insufficient vitamin C. Scurvy manifests through symptoms related to vitamin C’s role in collagen formation and antioxidant function.
Symptoms of scurvy include fatigue, weakness, and aching limbs. Individuals may also experience gum inflammation and bleeding, easy bruising, and poor wound healing. These signs arise because defective collagen synthesis compromises the integrity of connective tissues, including blood vessels and skin.
Our Dietary Solution
Given the body’s inability to synthesize vitamin C, humans rely entirely on their diet to meet their daily requirements. Fruits and vegetables are good sources of this essential nutrient. Examples include citrus fruits like oranges and grapefruits, as well as berries such as strawberries and blackcurrants.
Other rich sources include bell peppers, broccoli, Brussels sprouts, and potatoes. It is important to consume a balanced diet with a diverse range of produce to ensure adequate vitamin C intake. Cooking methods can also influence vitamin C content, as it is a water-soluble vitamin reduced by heat and prolonged water exposure.